Fix type error (#31999)

Signed-off-by: Adolfo Victoria <adolfokarim@gmail.com>
Co-authored-by: Adolfo Victoria <adovi@meta.com>

vllm/entrypoints/responses_utils.py

@@ -78,7 +78,9 @@ def _maybe_combine_reasoning_and_tool_call(
     This function checks if the last message is a reasoning message and
     the current message is a tool call"""
     if not (
-        isinstance(item, ResponseFunctionToolCall) and item.id.startswith(MCP_PREFIX)
+        isinstance(item, ResponseFunctionToolCall)
+        and item.id
+        and item.id.startswith(MCP_PREFIX)
     ):
         return None
     if len(messages) == 0: